Spur gear pumps conventionally include a housing including a gear chamber. The gear chamber may take on a variety of configurations from that of an oval to the shape of an eight and two meshed spur gears are received within such chamber. To one side of the point at which the gears mesh is an inlet port while on the opposite side of the point of meshing is an outlet port. At other locations about the periphery of the gears, the wall of the gear chamber is in close proximity to the teeth of the gears.
The gears are integral with or mounted on shafts journalled in bearings in the housings and upon rotation of one of the shafts, the gears will rotate in opposite directions. Fluid, normally in the form of a liquid, will be drawn in the inlet and carried by the spaces between the teeth of the gears around the chamber periphery to the outlet. As the teeth of the gear mesh adjacent the outlet, fluid is forced out of the spaces between the teeth under pressure and out the outlet.
By their very nature, gear pumps, and specifically the gears and shafts thereof, are side loaded. Low pressure will be present at the inlet side while high pressure will be present at the outlet side; and the high pressure acts against the gears generally in the direction of the inlet. As a consequence, the pressure tends to cause the shafts mounting the gears to deflect away from the outlet side of the pump.
The amount of shaft deflection is greater adjacent the gears than at locations on the shafts more remote from the gears and as a consequence, the thickness of any lubricant film between the bearings and the shaft journals is substantially reduced or eliminated altogether with the consequence that the bearing and shaft journals adjacent the gears are subject to high wear rates resulting in relatively short operational life of the pump and/or substantial down time.
The art has long recognized this problem and has proposed a variety of solutions including the use of self-aligning bearings, bearings mounted in resilient webs which in turn may deflect to allow the bearing to align with the shafts, and bearings which themselves may pivot to allow the maintenance of a lubricating film of sufficient thickness.
One long known attempt at the latter approach is the use of bearings or bushings for the shafts which have barrel-shaped exterior configuration. This approach is illustrated in, for example, U.S. Letters Patent No. 4,336,006 issued June 22, 1982 to Grabow et al. According to this approach, as the shafts deflect under side loading during operation of the pump, the bearings or bushings journalling the shafts may pivot within the housing to maintain proper journal-shaft alignment. Unfortunately, in most instances, the bearings or journals are provided with planar faces remote from the gears which, in turn, are in abutment with a planar surface of the pumping chamber. As a consequence, the contact between the two planar surfaces tends to resist such pivoting with the consequence that the barrel-shaped exterior configuration of the bushing is not as effective as is desired.
The present invention is directed to overcoming the above problem.